Ambrose of Milan : How indeed but in his body did Christ expiate the sins of the people? In what did he suffer, save in his body—even as we said: "Christ having suffered in the flesh"? In what is he a priest, save in that which he took unto himself the vocation of a priestly nation? — Exposition of the Christian Faith 3.11.86 Bede : The apostle Peter now rightly gives to the Gentiles this attestation of praise which formerly was given by Moses to the ancient people of God, because they believed in Christ, who like a cornerstone brought the Gentiles into that salvation which Israel had had for itself. He calls them "a chosen race" on account of their faith, that he may distinguish them from those who by rejecting the living stone have themselves become rejected. They are "a royal priesthood," however, because they have been joined to his body who is their real king and true priest, who as king grants to his own a kingdom and as their high priest cleanses them of their sins by the sacrificial victim of his own blood. He names them "a royal priesthood" that they may remember both to hope for an eternal kingdom and always to offer to God the sacrifices of a stainless way of life. — Commentary on the Catholic Epistles, 1 Peter 2:9